[PD-dev] PDINSTANCE for Pd (was Re: call for discussion double-precision file extension)

[Christof Ressi]

> I was thinking to a way for the transition: we could:
> - change the t_pdinstance pd_s_* fields to pointers (and adapt the s_* 
> replacement  macros accordingly),
> - export "hidden" globals s_*
> - initialize pd_maininstance pd_s_* fields to the global versions.
Yes, this would work. Of course, it would be an ABI break for 
multi-instance libpd, but I think it would be justified. I guess libpd 
users rarely rely on pre-build externals, and even if they do, I think 
it's ok to ask them to recompile.

We should probably also put the global s_* symbols in a deprecation 
macro that tells external authors to use gensym() instead.

Christof

On 04.04.2022 13:55, Antoine Rousseau wrote:
> I very much agree that in the future Pd (and externals) could be 
> always compiled with PDINSTANCE.
>
> I was thinking to a way for the transition: we could:
> - change the t_pdinstance pd_s_* fields to pointers (and adapt the s_* 
> replacement  macros accordingly),
> - export "hidden" globals s_*
> - initialize pd_maininstance pd_s_* fields to the global versions.
>
> CURRENT:
> /* m_pd.h */
> struct _pdinstance
> {
>     t_symbol pd_s_float;
> }
> #define s_float (pd_this->pd_s_float)
>
> /* m_class.c */
> t_pdinstance *pdinstance_init(t_pdinstance *x)
> {
>     dogensym("float",   &x->pd_s_float,    x);
> }
>
> PROPOSAL:
> /* m_pd.h */
> struct _pdinstance
> {
>     t_symbol  *pd_s_float;
> }
> #define s_float (*(pd_this->pd_s_float))
>
> /* m_class.c */
> #undef s_float
> t_symbol s_float;
> t_pdinstance *pdinstance_init(t_pdinstance *x)
> {
>     if(x != &pd_maininstance) x->pd_s_float = gensym("float");
>     else {
> dogensym("float",     &s_float,    x);
> x->pd_s_float = &s_float;
> }
>
> What do you think?
>
> I've tried this (in libpd context) almost successfully, but I've 
> encountered a problem: the s_float as seen from an app linked to libpd 
> seems to be uninitialized.
> I've tried something simpler:
> /* m_class.c */
> float myfloat = 10.0;
> t_pdinstance *pdinstance_init(t_pdinstance *x)
> {
> myfloat = 20.0;
> printf("pdinstance_init::myfloat: %f\n", myfloat);
> }
>
> /* pdtest.c */
> extern float myfloat;
> int main()
> {
>     libpd_init();
>     printf("myfloat: %f\n", myfloat);
> }
>
> cc -I../../../libpd_wrapper -I../../../pure-data/src -O3   -c -o 
> pdtest.o pdtest.c
> gcc -o pdtest pdtest.o ../../../libs/libpd.so
>
> $ pdtest
> pdinstance_init::myfloat: 20.00000
> myfloat: 10.00000
>
> Do you know why pdtest doesn't see the updated value?
>
> Le mer. 30 mars 2022 à 23:51, Christof Ressi <info at christofressi.com> 
> a écrit :
>
>     AFAICT, the main issue is that multi-instance Pd misses symbols for
>     certain global variables, most notably  s_float, s_symbol, s_bang,
>     etc.
>
>     The problem is that these are really exported global structs. If they
>     were *pointers*, we could simply make them point to the corresponding
>     field in the main Pd instance. But in this case I don't really see a
>     solution...
>
>     On 30.03.2022 18:07, IOhannes m zmoelnig wrote:
>     >
>     > On 3/30/22 17:45, Dan Wilcox wrote:
>     >> I lean much more on the side that PDINSTANCE is a low-level, per
>     >> project compile option and not general-purpose. If you are using
>     >> libpd, then your environment is a bit more custom anyway.
>     >
>     > i wonder what the penalty would be to turn on PDINSTANCE on Pd?
>     >
>     >
>     > obviously a problem with externals, but maybe we can come up
>     with some
>     > clever hack (under the assumption, that Pd (the app) only runs a
>     > single instance, even if compiled with multi-instance support)
>     to use
>     > legacy externals - if that is even possible.
>     >
>     > apart from that?
>     >
>     > fgadrms
>     > IOhannes
>     >
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